The present invention relates to a multifocal lens containing a holographic element and providing at least two optical powers.
Various bifocal lens design concepts for ophthalmic lenses, which are placed on or in the eye to correct visual defects, e.g., contact lenses and intraocular lenses, are available. One conventional bifocal ophthalmic lens design is the concentric simultaneous vision type. A concentric simultaneous bifocal lens has alternating optical zones that are concentrically placed. The concentric alternating optical zones have different radii of curvature to provide separate powers for near images and far images and, thus, focus near and far images onto a common focal region. Although concentric simultaneous bifocal lenses have been available for some time, they have not been used widely. This is because images projected on the retina by a concentric simultaneous bifocal lens are composed of both near and far images, and the overlapping images make neither of the near and far images completely clear. For example, when a distant object is viewed through a concentric simultaneous bifocal lens, images of near objects are simultaneously present, veiling or fogging the image of the distant object. In addition, because the light entering the concentric simultaneous bifocal lens is shared by the two optical zones, contrast and intensity of the focused images are sacrificed, especially under low light conditions.
Another conventional bifocal ophthalmic lens design is the diffractive simultaneous vision type. These lenses have a diffractive optical element and a refractive optical element, and utilize both optical elements to simultaneously project distant and near images on the retina. As with concentric simultaneous bifocal lenses, a diffractive simultaneous bifocal lens splits the light entering the eye into near and far images and projects the images simultaneously on the retina. Consequently, neither of the near and far images is completely clear and creates the contrast and intensity problem under low light conditions.
Yet another conventional bifocal ophthalmic lens design is the translating type. A translating bifocal constant lens generally follows the design of a conventional bifocal lens for eye glasses. A translating lens has two distinct localized viewing sections that have different optical powers. The position of the bifocal lens on the eye must shift from one section to the other when the wearer wishes to see objects that are located at a distance different from the objects currently in focus. One major problem inherent in a conventional translating bifocal ophthalmic lens is the difficulty encountered when the wearer tries to shift the position of the lens on the eye. The lens must move or shift a relatively large distance on the eye to change from one viewing section to the other, and the shift from one viewing section to the other must be complete before clear vision can be realized.
Recently, actively controllable approaches for providing a bifocal function in an ophthalmic lens have been proposed. A simultaneous vision type bifocal lens having sectionally applied thermochromic coatings is an example. The bifocal lens is designed to activate the thermochromic coating on the distant optical zone of the lens, when the wearer looks down to focus on a near object. The activated thermochromic section of the lens blocks light from going through the distant optical zone, thereby preventing the veiling or fogging affect of the light originating from near objects. This approach is not highly practical in that currently available thermochromic coating materials do not activate and deactivate fast enough for the concept to be practical. Another approach uses a lens that changes its focal length with an aid of a switchable battery or photocell. This approach also is not currently practical in that the electronic circuitry and the power source must be made small enough to be packaged in an ophthalmic contact lens and must be highly reliable and durable.
There remains a need for an ophthalmic lens that reliably provides multifocal functions without the deficiencies of prior art multifocal lenses. There additionally remains a need for optical materials that can be easily processed to produce a holographic optical element.